Pat ribeyes dry with a paper towel and season with cajon seasoning, salt, and pepper. Allow to dry brine in the refrigerator for up to 24 hours. Then slice into thin strips and set aside.
Slice bell peppers and onions and set aside.
Add olive oil, butter, and thyme to a skillet over high heat. Allow oil to warm for 2-3 minutes then add ribeye and sear for about 4-5 minutes, until a crust forms. Remove and set aside to rest.
Reduce heat to medium and add bell peppers and onions to the pan and cook for about 8-10 minutes, until peppers soften but aren't mushy. Remove and set aside.
Combine ingredients for remoulade in a small bowl and whisk together.
Slice ciabatta buns in half and add to the skillet to toast for a few minutes. Lather with remoulade and add arugula and bell peppers and onions. Then add sliced ribeye and close sandwich.